When working the satellites FO-20 and FO-29, the uplink is on 2m and the
downlink is on 70cm. If, like my setup, the beams are close together (mine are about 4ft
apart) then there can be desensing caused to the 70cm RX when TX on 2mtr. Also it can
cause strong 'hash' to be heard on the 70cm downlink, especially when running a Preamp.

This QRM needs to be eliminated as much as possible as it is important to hear
ones own downlink to determine the quality of the signal, correct tuning for doppler
shift, etc. My simple aerial system doesn't allow the beams to be spaced any further
apart so I had thought of buying, or building a cavity type filter for the 70cm RX when a
regular satellite contact of mine
(Mike KF4FDJ)
suggested trying a 2m / 70cm duplexer - just using the 70cm section.

I had a Watson WD-24N which I had never used and tried the idea out.
First I changed the pl259 input plug to an "N" type socket then plugged
the duplexer into the 70cm feeder just before the signals enter the Preamp. In my case
this is in my linear amp in the shack. It worked well, eliminating most problems
with less loss than a tighter tuned filter. (Insertion loss stated as 0.2db)

I would not have thought of trying the duplexer without Mike's suggestion, and
pass on this idea to any others whose lateral thinking may be as narrow as mine ;-)